The benzoxazinone compounds according to the present invention are represented by the formula (I): ##STR2## wherein R.sup.1 represents a hydrogen atom or an alkyl group, and R.sup.2 represents a hydrogen atom, an alkyl group, a cyanoalkyl group, an alkenyl group, an alkynyl group or an aralkyl group.
Hitherto, various types of oxazolidinedione compounds having a substituent at the 5-position of the oxazolidinedione ring have been known, but oxazolidinedione compounds having a substituted methylidene group at the 5-position have not been reported in view of the fact that the synthesis of these compounds has been considered very difficult. Further, although various types of heterocyclic compounds having a herbicidal activity have been reported in various publications and have been practically used to date, no oxazolidinedione type compounds have been known to have a practically useful herbicidal activity.
Of the conventionally known oxazolidinedione compounds, compounds having a substituted or unsubstituted phenyl group on the nitrogen atom at the 3-position and having an alkylidene group at the 5-position have been reported to have a herbicidal activity against various weeds as described in Japanese Patent Application (Kokai) No. 62-174065 (the term "Kokai" as used herein means an unexamined published application), but this prior art reference does not teach or suggest the physiological activity of compounds having a bicyclic substituted phenyl group such as a compound having a benzoxazinone ring.
As a result of extensive studies on various oxazolidinedione derivatives, the present inventors found that these novel oxazolidinedione compounds having an isopropylidene group at the 5-position and having a substituted benzoxazine on the nitrogen atom at the 3-position, i.e., the benzoxazinone compounds represented by the formula (I) above, exhibit a strong herbicidal activity against various weeds at a relatively low dose and can be practically used as a herbicidal agent. On this basis they completed the present invention.